NASA's Interplanetary Boundary Explorer (IBEX), which is a spacecraft designed to study the interaction of the solar wind with the Galaxy's interstellar gas, is set to launch this Sunday, October 19, at 1:48 p.m. Eastern Daylight Time. The spacecraft is mounted to a Pegasus XL rocket, which will be launched from a L-1011 aircraft flying out of the Kwajalein Atoll in the Marshall Islands. Live streaming video of the launch will be available at the NASA home page.
The Sun expels a high-velocity wind. This wind interacts with the interstellar medium far outside of the solar system where the ram pressure of the solar wind equals the pressure of the interstellar medium. This interaction produces two standing shockwaves sandwiching a teardrop-shaped shell of hot gas. The outer shockwave, called the bow shock, is where the interstellar gas interacts with the hot shell; this shock wave gives the hot shell its teardrop shape because the Sun is moving relative to the interstellar medium. Its closest point is about 200 AU from Earth. The inner shock, called the termination shock, is where the solar wind interacts with the hot shell. It has a radius of about 100 AU.
The small IBEX spacecraft, which will be in a high-altitude orbit around Earth, has two instruments that detect high-energy neutral atoms accelerated in the termination shock and flying through space to Earth. The instruments will generate a full map of the termination shock after six months of detecting the neutral atoms. The IBEX mission is planned to last 2 years.